1. Field of the Invention
The present invention relates to a dithering mask used in displaying images and a method of forming the same, and more particularly, to a dithering mask that can avoid generating flick patterns on a screen, and a method of forming the dithering mask.
2. Description of the Prior Art
Dithering, which is a technique to display halftone, places pixels with two gray levels in specific positions to create the visional illusion in human eyes that a third gray level between the two gray levels is present, thereby achieving a dithering effect in the space domain. Another way to obtain the dithering effect is in the time domain by rotating a dithering mask so that points in the dithering mask switch rapidly between different gray levels.
The above-mentioned dithering techniques, however, may generate flick patterns or unexpected patterns (such as a particularly bright line or a rolling bright line) on the screen in some situations. For example, please refer to FIG. 1A-FIG. 1D. As shown in FIG. 1A, the screen only regularly displays two pixels of four adjacent pixels (the pixels not displayed are shown with oblique lines in FIG. 1A; that is, the contents of the pixels 130 and 140 are shown in the display screen, while the contents of the pixels 110 and 120 are not shown), and the dithering result is that the pixels 130, 150, 160 and 170 have a higher gray level A, and the other pixels have a lower gray level B. After being processed by the above-mentioned time domain rotation as shown in FIG. 1B, the pixels having higher gray level A are all rotated to the non-displayed positions. Therefore, the illumination of the screen in FIG. 1B becomes darker than the preceding screen, i.e., the screen in FIG. 1A. Next, when the screen in FIG. 1B is rotated, generating screen in FIG. 1C, and the screen in FIG. 1C is further rotated to generate screen in FIG. 1D, the illumination of the screen in FIG. 1D is brighter than the preceding screen since the pixels having the higher gray level A are rotated back to the display positions. The variation of the illumination of the display screen causes a flicker phenomenon noticeable to human eyes, and deteriorates the display quality of the screen.